Aircraft engine fuel system

Abstract

A fuel system for a gas turbine aircraft engine including a ecology valve and a flow divider valve, both of simple and compact construction. The ecology valve is connected to the fuel manifolds supplied by the splitter valve, and serves to suction fuel from the fuel manifolds upon engine shutdown. The fuel is temporarily stored in reservoirs in the ecology valve and upon the next engine operating cycle, is returned to the manifold so that it can be burned. The splitter valve is of simplified light-weight construction and includes a single piston operated in two regions, a first for modulating primary and second flow depending on fuel pressure, and a second region for providing a fixed, port geometry determined split between the primary and secondary.

What is claimed is: 
     
       1. A fuel system for use in an aircraft engine, the fuel system comprising: a fuel pump for pressurizing fuel from a fuel supply, a plurality of fuel nozzles arranged in a combustion chamber, a fuel metering unit for controlling the flow of fuel from the fuel pump to the fuel nozzles,   a fuel manifold fluidically connecting the fuel metering unit to the fuel nozzles, and   an ecology valve fluidically connected to the fuel manifold, the ecology valve having a reservoir for temporary storage of fuel, and reservoir control means for suctioning sufficient fuel into the reservoir to prevent coking of the nozzles upon engine shutdown for temporary storage and return of the temporarily stored fuel for combustion in the next engine operating cycle.   
     
     
       2. The fuel system as defined in claim 1, wherein: the reservoir has sufficient capacity to receive and temporarily store a volume of fuel at least equal to the volume of fuel remaining in the fuel manifold upon engine shut-down; and   the reservoir control means varies the volume of the reservoir to suction fuel from the manifold upon engine shut-down and to return of fuel to the fuel manifold upon engine start-up.   
     
     
       3. The fuel system as defined in claim 2, further comprising: a flow divider valve arranged downstream of the fuel metering unit; and wherein:   the fuel nozzles comprise a primary set and a secondary set;   the fuel manifold comprises a primary manifold and a secondary manifold, the primary manifold fluidically connecting the flow divider valve to the primary set of fuel nozzles and the secondary manifold fluidically connecting the flow divider valve to the secondary set of fuel nozzles; and   the reservoir comprises first and second storage chambers fluidically connected to the primary and secondary fuel manifold, respectively.   
     
     
       4. The fuel system as defined in claim 3, wherein the first storage chamber accommodates a volume of fuel equal to the capacity of the primary fuel manifold and the second storage chamber accommodates a volume of fuel equal to the capacity of the secondary fuel manifold. 
     
     
       5. The fuel system as defined in claim 3, wherein the reservoir control means comprises a pressure chamber in the ecology valve having a control port connected to the fuel metering unit to sense pressure in the fuel supply, and pressure sensing means in the pressure chamber for returning fuel to the manifold when the fuel pressure is high and suctioning fuel from the manifold as the fuel pressure decreases on engine shutdown. 
     
     
       6. The fuel system as defined in claim 5, wherein the pressure responsive means includes a piston having an operating face disposed in the pressure chamber and an opposite face defining the reservoirs, a skirt portion carried by the opposite face to divide the reservoir into two separate chambers for the primary and secondary manifolds. 
     
     
       7. The fuel system as defined in claim 6, wherein the reservoir control means further includes spring means for biasing the piston in a direction to fill the reservoirs, the pressure chamber being disposed opposite the spring for overcoming the bias to expel fuel from the reservoirs as the fuel pressure increases upon engine start up. 
     
     
       8. The fuel system as defined in claim 7, wherein the reservoir control means slowly translates the piston to slowly expand the reservoirs and create a suctioning effect adequate to draw fuel from the respective manifolds. 
     
     
       9. The fuel system as defined in claim 8, including orifice in the connections between the manifolds and the respective reservoirs for controlling the rate of fuel transfer into and out of the reservoirs, and a further flow control orifice between the fuel line and the pressure chamber for controlling the rate of piston travel. 
     
     
       10. The fuel system as defined in claim 3, wherein the flow divider valve includes: a flow divider valve body and a ported piston mounted for translation in the valve body;   means biasing the ported piston to a quiescent condition in which flow to the primary and secondary manifolds is shut off;   the body and ported piston establishing two operating regions for the flow divider valve;   ports in the body and piston effective with the piston in the first region for modulating primary flow as a function of inlet fuel pressure;   a relief valve in the piston for diverting a portion of the modulated primary flow to the secondary as a function of the pressure differential in the primary and secondary manifolds;   means activated by continued piston travel from the first toward the second regions for sharply translating the piston to a final operating position in the second region; and   ports in the body and piston effective with the piston in the second region for providing a fixed unmodulated split of flow through the divider valve to the primary and second manifolds.   
     
     
       11. An ecology valve for use in an aircraft engine fuel system, the fuel system comprising a fuel pump for pressurizing the fuel in a fuel supply, a fuel metering unit for modulating the fuel flow rate from the fuel supply to a primary and secondary set of fuel nozzles, and a primary and secondary fuel manifold fluidically connecting the fuel metering unit to the primary and secondary fuel nozzles, respectively, the ecology valve comprising: a valve body;   a pressure actuated piston slidably disposed within the valve body and movable between an unloaded position corresponding to engine shut-down and a loaded position corresponding to engine operation, the piston having a pressure face on one side and an annular skirt on the other side;   spring means for biasing the piston toward the unloaded position;   the valve body cooperating with the skirt portion of the piston to create a first and second storage reservoir separated by the skirt portion and connected to the primary and secondary manifolds, respectively, translation of said piston sensing to increase or decrease the size of the respective reservoirs for accepting fuel from or returning fuel to the respective manifolds;   the valve body and pressure face of the piston creating a pressure chamber fluidically connected to the fuel metering unit for responding to the pressure level in the fuel supply; and   whereby movement of the piston from the loaded position to the unloaded position during engine shut-down suctions fuel from the primary and secondary manifolds to the first and second storage chambers, respectively, and movement of the piston from the unloaded position to the loaded position during engine start-up drives fuel from the first and second storage chambers to the primary and secondary fuel manifolds, respectively.   
     
     
       12. A flow divider valve for use in an aircraft engine fuel system, the fuel system comprising a fuel pump for pressurizing fuel from a fuel supply, a primary and a secondary set of fuel nozzles arranged in a combustion chamber, a fuel metering unit for controlling the flow of fuel from the fuel pump to the fuel nozzles, primary and secondary fuel manifolds fluidically connecting the flow divider valve to the primary and secondary fuel nozzles, respectively, and a fuel line fluidically connecting the fuel metering unit to the flow divider valve, the flow divider valve comprising, in combination: a flow divider valve body and a ported piston mounted for translation therein;   means biasing the ported piston to a quiescent condition in which flow to the primary and secondary manifolds is shut off;   the body and ported piston establishing two operating regions for the valve;   ports in the body and piston effective with the piston in the first region for modulating primary flow as a function of inlet fuel pressure;   a relief valve for bypassing the piston for diverting a portion of the modulated primary flow to the secondary as a function of the pressure differential in the primary and secondary manifolds;   means activated by continued piston travel from the first toward the second regions for sharply translating the piston to a final operating position in the second region; and   ports in the body and piston effective with the piston in the second region for providing a fixed unmodulated split of flow through the divider valve to the primary and second manifolds.   
     
     
       13. The flow divider valve as defined in claim 12, wherein the relief valve comprises a spring biased relief valve formed in the face of the piston for porting fuel through the face of the piston when the differential between the primary and second manifolds exceeds the pressure exerted by the spring bias. 
     
     
       14. The flow divider valve as defined in claim 12, wherein the relief valve is a separate valve interconnected between the primary and secondary manifolds. 
     
     
       15. The flow divider valve as defined in claim 12, wherein the means activated by continued piston travel comprises a porting arrangement between the first and second regions which temporarily interrupts primary flow to thereby temporarily increases pressure driving the piston to the second region. 
     
     
       16. The flow divider valve as defined in claim 15 wherein the porting arrangement between the first and second regions is positioned to equalize pressure in the primary and secondary manifolds whenever pressure in the secondary manifold attempts to exceed pressure in the primary manifold. 
     
     
       17. The flow divider valve as defined in claim 15 wherein the porting arrangement between the first and second regions is positioned to provide a minimum flow in the primary manifold under all conditions of discharge flow. 
     
     
       18. A method for ecologically regulating fuel flow in an aircraft engine fuel system, the fuel system comprising a fuel pump for pressurizing fuel from a fuel supply, a plurality of fuel nozzles arranged in a combustion chamber, a fuel metering unit for controlling the flow of fuel from the fuel pump to the fuel nozzles, and a fuel manifold fluidically connecting the fuel metering unit to the fuel nozzles, the method comprising the steps of: providing a temporary sump connected to the fuel manifold;   suctioning sufficient fuel into the sump upon engine shut-down to prevent coking of the nozzles;   temporarily storing the fuel in the sump while the engine is inoperative; and   returning the stored fuel from the sump to the fuel system during the next engine start-up.   
     
     
       19. A fuel system for use in an aircraft engine, the fuel system comprising: a fuel pump for pressurizing fuel from a fuel supply, a plurality of fuel nozzles arranged in a combustion chamber, a fuel metering unit for controlling the flow of fuel from the fuel pump to the fuel nozzles;   a fuel manifold fluidically connecting the fuel metering unit to the fuel nozzles;   an ecology valve fluidically connected to the fuel manifold, the ecology valve having a reservoir for temporary storage of fuel in the manifold, reservoir control means for suctioning sufficient fuel from the manifold into the reservoir upon engine shut-down to prevent coking of the nozzles and for temporary storage and return of the temporarily stored fuel to the manifold for combustion in the next engine operating cycle;   the reservoir having sufficient capacity to receive and temporarily store a volume of fuel at least equal to the volume of fuel remaining in the fuel manifold upon engine shut-down; and   the reservoir control means varying the volume of the reservoir to suction fuel from the manifold upon engine shut-down and for return of the fuel to the manifold upon engine start-up.   
     
     
       20. An ecology valve for use in an aircraft engine fuel system, the fuel system having a fuel pump for pressurizing the fuel in a fuel supply, a fuel metering unit for modulating the fuel flow rate from the fuel supply via a manifold to a set of fuel nozzles, the ecology valve comprising: a reservoir connected to the fuel manifold for temporary storage of fuel; and   reservoir control means for suctioning sufficient fuel into the reservoir to prevent coking of the nozzles upon engine shut-down for temporary storage and return of the temporarily stored fuel for combustion in the next engine operating cycle.